12AU7 and 12AX7 long black plates vs short black plates. Any difference ?

joeycastillo, yes, it appears to be a consensus here that long black plates, both 12AU7 and 12AX7, are overall better sounding, regardless of particular equipment. They deliver the most authentic sound.

When it comes to military/industrial substitutes for them the picture might be a little less clear. I intend to try Sylvania 5814A triple mica and perhaps RCA 5814A triple mica at some point. Other than that there is probably no reason for me to try anything else.

@inna 

"12AU7 and 12AX7 long black plates vs short black plates. Any difference ?"

Microphonics. @mulveling goes on about it -

"Bigger plates can mean more microphony too, though. The way these things are suspended in the glass envelope makes them a vibration antenna, and the mica spacers have to retain a tight grip over all these years & heat/cool cycles."

@mulveling 

"And with a tube power amp or integrated, the vast majority of heater draw is from the power tubes. You're getting into a fractional % of a delta on the filament tap from this."

To elaborate -

The small signal tube heater supplies AC or DC are taken from a separate winding on the power transformer and in the case of DC a separate rectifier bridge and ancillary components to present clean power to the filaments at 6 or 12 volts.

Hi Joecastillo, i also concur - just wish we had measurements to demonstrate this, ie 3s soundstage, musicality etc.

Do long black plates with square getter, usually earlier production, sound slightly better than with D getter ? I understand, this might be going into extreme details, but we are high end and small is big for us.

Just compared this. I did not hear any difference between square and D getter Sylvania 12au7 long black plates from 1950s. This does not necessarily mean that you wouldn't. Besides, VAC Avatar SE is an excellent amp but I consider it audiophile entry level.